Metal-organic frameworks in chromatography

Accepted Manuscript Title: Metal-Organic Frameworks in Chromatography Author: Kareem Yusuf Ahmad Aqel Zeid ALOthman PII: DOI: Reference:

S0021-9673(14)00699-2 http://dx.doi.org/doi:10.1016/j.chroma.2014.04.095 CHROMA 355387

To appear in:

Journal of Chromatography A

Received date: Revised date: Accepted date:

17-2-2014 14-4-2014 28-4-2014

Please cite this article as: K. Yusuf, A. Aqel, Z. ALOthman, MetalOrganic Frameworks in Chromatography, Journal of Chromatography A (2014), http://dx.doi.org/10.1016/j.chroma.2014.04.095 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Review

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Metal-Organic Frameworks in Chromatography

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Kareem Yusuf*, Ahmad Aqel, Zeid ALOthman

Riyadh 11451, Kingdom of Saudi Arabia.

∗ Corresponding author. Tel.: +966 596245977, E-mail address: [email protected].

ABSTRACT

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Metal-organic frameworks (MOFs) emerged approximately two decades ago and are

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the youngest class of porous materials. Despite their short existence, MOFs are

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finding applications in a variety of fields because of their outstanding chemical and

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physical properties. This review article focuses on the applications of MOFs in

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chromatography, including high-performance liquid chromatography (HPLC), gas

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chromatography (GC), and other chromatographic techniques. The use of MOFs in

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chromatography has already had a significant impact; however, the utilisation of

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MOFs in chromatography is still less common than other applications, and the number

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of MOF materials explored in chromatography applications is limited.

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(2D) and frameworks (3D) [3].

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The term coordination polymers (coordination networks) was previously used to

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describe MOFs [4-8] due to their similarity with coordination chemistry, especially

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the polyhedral inorganic parts [3]. The differences in vocabulary are usually due to

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the researchers who created the structures, although they are almost using the same

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types of materials [9]. However, Tranchemontagne et al. identified distinct differences

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Advanced Materials Research Chair, Department of Chemistry, College of Science, King Saud University, P.O. Box 2455,

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1. Introduction

Metal-organic frameworks (MOFs) are crystalline, highly ordered framework systems synthesised via the self-assembling combination of organic ligands and inorganic metals or metal-oxo units (secondary building units, SBUs) using strong bonds to form a permanent, porous open crystalline framework [1, 2]. The inorganic part of MOFs could be selected with various dimensionalities, creating chains (1D), layers

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between coordination polymers and MOFs [10]. Since the term “MOF” was

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introduced in 1995 by Yaghi and co-workers [11], there has been intensive research

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that led to approximately 20,000 different MOFs over the past two decades [1].

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In comparison to conventional porous inorganic frameworks, such as zeolites or

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carbon-based materials, the active surface areas of MOFs are considerably large,

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reaching 7140 m2.g-1 [12]. Inorganic frameworks also have limited diversity because

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they accept only a few cations [13-19], mostly limited to Al, Si and chalcogens [20],

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whereas MOFs exist with almost all possible cations up to tetravalent atoms [3]. The

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variety of elements used in MOFs, along with the large choice of organic linkers,

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provides a substantial number of possibilities for creating new MOFs. Conversely,

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inorganic frameworks often utilize a variety of templates or structure-directing

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compounds. These templates are removed via oxidation, and as a consequence, the

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removal of the template can result in the collapse of the framework. In MOFs, the

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framework template is directed by the SBU and the organic ligands [21, 22].

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MOFs hold the world records for the most porous materials with the largest pore

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aperture (98 Å) [23], the highest specific surface area (10400 m2.g-1) [12] and the

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lowest density (0.13 g.cm-3) [24]. MOF structures have synthetic flexibility to change

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their size and nature without changing their topology, which is called the isoreticular

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principle (from the Greek term iso meaning same and the Latin term reticulum

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meaning net). The isoreticular character allows MOFs to hold macromolecules, such

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as vitamins and proteins, and to increase the interaction space within the pores. The ability of adding functional groups into the framework also give MOFs another advantage over other porous materials by allowing post-synthetic modification [1]. The designable structures of MOFs, along with their unique physical, thermal and chemical properties, have led to their utilisation in numerous applications, including chromatographic applications.

2. Structural overview

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Metal-organic frameworks consist of two main components: a metal-containing

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component (cationic part) and an organic component (anionic part) that combine

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through strong bonding to produce a well-defined highly ordered framework [25].

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One of the main properties of MOFs is self-assembly, which affords the desired 2 Page 2 of 52

structure framework. Self-assembly is defined by George Whitesides as “a process

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where pre-designed components assemble in a determined structure without the

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intervention of human operators” [26]. The important characteristics of the metal-

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containing part are their coordination numbers and geometries, which play an

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important role in directing the MOF structures. The other important property is the

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organic linkers, which have a great influence over the shape of the constructed MOF.

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The organic linkers (or ligands) generally contain coordinating functional groups,

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such as carboxylates, phosphates, sulphonates, amines, or nitriles, which serve an

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essential function in locking the metal ions strongly into their positions. Figure 1

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shows some examples of such organic linkers in MOFs [27].

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It is difficult, but not impossible, to obtain such MOF structures from simple metal

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ions and organic linkers because the ions provide little directionality [27]. This limited

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directionality results in mobility around the metal ion and more than one possible

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structure, which yields generally inconsistent results, as exemplified by the

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frameworks based on Cu ions and bipyridine and related linkers [28-35].

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To design a network molecular structure such as a MOF, we can start with well-

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defined and rigid molecular building blocks (MBBs) that will maintain their structure

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during the construction process [36, 37]. Alternatively, the use of well-defined

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reaction conditions to form these building blocks in situ is an equally applicable

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method to design this type of extended structure, which is called reticular synthesis

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[37]. Yaghi et al. described reticular synthesis as “the process of carefully designing a rigid molecular building blocks into stable highly ordered networks, which are held together by strong bonding” [27]. Reticular chemistry [38] - sometimes referred to as ‘crystal engineering’ - is concerned with the design and synthesis of compounds formed from finite SBUs joined by strong chemical bonds [27]. SBU is an abbreviation that refers to the geometry of the building units defined by the points of extension and describes either the organic or inorganic part of the MOF structure [27].

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In reticular synthesis, the metal-containing (cationic) SBUs cannot be isolated, so they

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have to be constructed in situ with careful control over the reaction conditions,

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including the mixing stoichiometry, reaction temperature and time, solvent system,

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ionic strength and concentration, addition of weak acids or bases and the nature of the

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counter ions [27]. Conversely, organic (anionic) SBUs are pre-synthesised using

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conventional organic synthetic methods [39]. A basic prediction supported by 3 Page 3 of 52

experimental results [40] is that when symmetrical SBUs are attached to simple

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linkers, only one high symmetry structure will be formed [41, 42]. In other words, by

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using such a strategy to synthesise MOF structures, it is possible to control and predict

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the structure of the resulting framework as well as its properties for a specific

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application [27].

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Crystal structures have been described in terms of nets since the beginning of

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crystallography. In these nets, atoms are the vertices and the bonds are the links

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(edges) between them. These nets are a special type of periodic graph [43]. In

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structures such as those of zeolites [44], tetrahedrally coordinated atoms (Si, Al, P

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etc.) are joined by –O– links to form a four-coordinated net of tetrahedral vertices

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with the –O– links acting as the edges [10]. In the case of MOFs, polyatomic groups

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act as the vertices and edges of the net [45].

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In 2000, O’Keeffe et al. [41] defined some topological rules for controlling the

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structures of porous solids, including MOFs. Starting with some MOF structures that

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correspond to extended versions of simple structures (diamond, sodalites, etc.), they

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developed a system of symbols for naming, classifying and identifying these

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topological structures based on the invariance of the topology of structures for any

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chemical associations, and this system is now in wide use. In this work, O’Keeffe and

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his group outlined the rules for the Reticular Chemistry Structure Resource (RCSR),

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which collected approximately 1600 structures in a database searchable by symbol,

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previous description of SBUs was revealed in MOF-2 [47] and MOF-5 [48]. In MOF-

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5, there are Zn4O(CO2)6 units containing four ZnO4 tetrahedra with a common vertex

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and six carboxylate C atoms that define an octahedral SBU, each linked by six

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chelating 1,4-benzenedicarboxylate (BDC) units, to give a cubic framework. In MOF-

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5 (a cubic network), the vertices are the octahedral SBUs, and the edges are the

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benzene molecules. The resulting structure was found to have an exceptional porosity

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name or keywords [45]. In the RCSR, the net topologies of the MOFs are described using a three-letter symbol in bold lower-case; the symbol is either a three-letter symbol (such as pqr) or a three-letter symbol with an extension as in pqr-a, which is called the augmented net in which a cluster of vertices replaces the vertex of the original net [46].

The first major breakthrough toward the design of rigid frameworks based on the

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of 61% (indicated by its gas sorption measurements), stability (indicated by thermal

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analysis and single crystal X-ray diffraction studies) and a high surface area of 2320

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m2.g-1 (indicated by Brunauer-Emmett-Teller, BET, measurements) [48]. These

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values are much higher than the conventional counterparts, such as zeolites and

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activated carbon [49]. The polyatomic cationic rigid clusters that form the vertices of

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MOF-5 could explain its exceptional stability [27].

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Changing the chemical composition, functionality, and molecular size of crystalline

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materials in a systematic way that maintains the topology was a challenge for material

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scientists [38, 50]. In 2002, Eddaoudi et al. [51] presented the first isoreticular [IR]

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structures based on the cubic pcu skeleton of MOF-5 (IRMOF-1) up to IRMOF-16

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with a 16-member family. The isoreticular structures of MOFs differ in the nature of

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the functional groups within the organic linker and/or in the length of its edges by

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using an expanded version of the organic linker without changing the original network

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topology.

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In IRMOF-2 through IRMOF-7, BDC links with R groups representing bromo,

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amino, n-propoxy, n-pentoxy, cyclobutyl, or fused benzene functional groups (Figure

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1) result in structures with almost the same size but different functionalities within the

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voids, whereas in IRMOF-8 (2,6 NDC linker; 2,6-naphthalenedicarboxylate) through

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IRMOF-16, pore expansion occurs due to the use of progressively longer organic

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linkers. However, the large space in the expanded forms tends to form

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interpenetrating structures, which indicates that two or more frameworks grow and interfere with each other. Figure 1 shows the absence of IRMOF-9, IRMOF-11, IRMOF-13, and IRMOF-15 due to interpenetration. These MOFs used BPDC (biphenyl-4,4'-dicarboxylate), HPDC (4,5,9,10-tetrahydro-2,7-pyrenedicarboxylate), PDC (2,7-pyrenedicarboxylate), and TPDC (p-terphenyl-4,4''-dicarboxylic acid) as linkers, respectively. The degree of interpenetration could be controlled by changing the reactant concentrations and reaction conditions. Non-interpenetrating counterparts

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have been successfully achieved for all linkers in the previous work by using diluted

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reaction conditions.

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Another effective way to prevent interpenetration is to select a suitable topology for

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MOFs that inhibits interpenetration [52]. MOF-177 [Zn4O(BTB)2] (BTB; 4,4',4''-

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benzene-1,3,5-triyl-tribenzoate) is a good example of interpenetration inhibition by 5 Page 5 of 52

using a triangular organic linker, giving rise to the qom net structure. Even in the case

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of the expanded isoreticular structures of MOF-177, which yields MOF-180

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[Zn4O(BTE)2] (BTE; 4,4',4''-(benzene-1,3,5-triyl-tris(ethyne-2,1-diyl))tribenzoate)

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and MOF-200 [Zn4O(BBC)2] (BBC; 4,4',4''-(benzene-1,3,5-triyl-tris(benzene-4,1-

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diyl))tribenzoate) [53], the networks remain non-interpenetrating despite the high

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porosity of these MOFs (89% and 90% for MOF-180 and MOF-200, respectively).

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Another interesting MOF is known as HKUST-1 [Cu3(BTC)2] (BTC; 1,3,5-benzene

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tricarboxylate) [54]; it is composed of Cu paddlewheel [Cu2(CO2)4] SBUs and a

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tritopic organic linker, BTC. Many isoreticular structures have been produced using

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several tritopic linkers to give the same tbo net structure of HKUST-1 [24, 55- 58].

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MOF-399 [Cu3(BBC)2] is the largest member of this family. Its cell volume is 17.4

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times that of HKUST-1. MOF-399 has the highest void fraction (94%) and the lowest

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density (0.126 g.cm-3) of any reported MOF [24]. Isoreticular structures can also be

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synthesised using different metal ions to afford the same network structure. The

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HKUST-1 isoreticular series was prepared by replacing the Cu metal ion with another

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metal, such as Zn(II) [59], Fe(II) [60], Mo(II) [61], Cr(II) [62], or Ru(II) [63].

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The superior adsorption ability of MOFs has been observed in gas storage and gas

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separation applications. The primary adsorption sites for Ar and N2 within the internal

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surface of the large-pore open MOF-5 have been identified using single-crystal x-ray

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diffraction [64]. The study revealed a total of eight adsorption sites. The adsorption

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sites included the zinc oxide units Zn4O(CO2)6, the faces, and the organic linker edges. Furthermore, it has been revealed that using tritopic organic linkers based on alkyne rather than phenylene groups will increase the adsorption sites and consequently increase the surface area [65]. Using such organic linkers led to NU-110 [Cu3(BHEHPI);

BHEHPI

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5,5',5''-((((benzene-1,3,5-triyltris(benzene-4,1-

diyl))tris(ethyne-2,1-diyl))-tris(benzene-4,1-diyl))tris(ethyne-2,1diyl))triisophthalate], which has the largest surface area of a porous material to date

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with a surface area of 7140 m2.g-1 [1].

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Using the BET method to calculate the surface area per unit weight of microporous

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materials, such as MOFs, is widely accepted [66]. However, a major problem

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accompanied with using this method is that separating the processes of mono-

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multilayer adsorption from micropore filling is difficult [67]. Therefore, the surface 6 Page 6 of 52

areas of MOFs obtained using the BET method are thought to not reflect the true

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internal surface area but rather should be considered a type of “apparent” or

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“equivalent BET area” [68, 69]. Recently, a simulation study was performed to test

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the applicability of the BET method for determining the surface areas of MOFs [70,

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71]. The BET surface areas from the simulated isotherms agreed with the

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experimental surface areas reported in the literature. For many practical applications,

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such as gas storage and gas separation, calculating the surface area per volume is

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more useful [1]. When we used this fact, we found that MOF-5 with a surface area of

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2200 m2.cm-3 is the best MOF material for such purposes, compared with NU-110,

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which has a surface area of 1600 m2.cm-3.

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The unique properties and the wide structural choices make MOFs attractive

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candidates for chromatographic applications (Table 1). Over the last few years, a

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substantial number of studies have demonstrated the potential of MOFs as a new class

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of chromatographic materials in the areas of gas and liquid chromatography. Yet only

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two specific review articles on the application of MOFs in separation science have

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been published [72, 73] .MOFs have been either directly used without further

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modifications or engineered to meet the chromatographic challenges. They have been

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used as column packings, coatings or as a monolithic material in conventional or

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capillary columns. This work focuses on the use of MOF materials in

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chromatographic applications.

3.1 Gas chromatography applications Gas chromatography (GC) is the most promising among the chromatographic techniques for employing MOFs as the stationary phase. Various MOF materials and column structures have been demonstrated in several publications for high resolution gas chromatography. In the following section, we will discuss the most significant and

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recent applications of MOFs in GC.

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3.1.1 Packed columns

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In 2006, Chen et al. introduced the first application of MOFs as a packing material in

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GC [74]. They used MOF-508 [Zn(BDC)(4,4'-Bipy)0.5(DMF)(H2O)0.5] with a thermal

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stability of up to 360°C as stationary phase for packed-column GC. A 120-cm 7 Page 7 of 52

chromatographic column, packed with single crystals of MOF-508 with sizes of 25-

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100 μm (3 g), was used in the study. The GC separation of natural gas was performed

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at an inlet pressure of 60 psi with helium as the carrier gas over a temperature range of

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40-150°C (Figure 2). The unique features of MOF-508 are its 1D pores of 4.0 × 4.0 Å,

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which separate linear alkanes from branched alkanes.

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The separation of isomers was investigated for the first time using a column packed

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with a MOF material by Finsy et al. [75]. They studied the separation of the C8 alkyl

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aromatic components p-xylene, m-xylene, o-xylene, and ethylbenzene (EB) on the

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metal-organic framework MIL-47 [VIVO(BDC)] using vapour-phase adsorption and

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separation. The four isomers were found to have comparable Henry constants and

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adsorption enthalpies at temperatures between 230 and 290 °C. The adsorption

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capacity of the adsorption isotherms were strongly temperature dependent at 70, 110,

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and 150 °C. The adsorption selectivity generally increases as the partial pressure or

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degree of pore filling increases. The separation at a high degree of pore filling in the

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vapour phase is the result of differences in the packing modes of the C8 alkylaromatic

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components in the pores of MIL-47.

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Gu et al. examined the adsorption and separation of xylene isomers and EB on two

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Zn−terephthalate MOFs (MOF-5 and MOF-monoclinic; [Zn4O(BDC)3]) using pulse

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gas chromatography, static vapour-phase adsorption, and breakthrough adsorption

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[76]. The two studied Zn−terephthalate MOFs, which showed different selectivities

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and efficiencies for the separation of xylene isomers and EB. Pulse GC experiments showed efficiency separation on MOF-5 (267 plate/m) than MOF-monoclinic (76 plates/m). On MOF-5, EB eluted first, while the other isomers eluted at the same time. The monoclinic MOF showed a preferable adsorption of p-xylene over the other isomers. The selectivity resulted mainly from the different sizes of pore windows in the Zn-terephthalate MOFs. The terephthalate linkers in MOF-5 form pores with a

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cross section approximate 12 Å in size. Therefore, the four isomers gave similar

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diffusion coefficients on MOF-5 without any size hindrance with respect to the kinetic

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diameters of xylene isomers and EB (5.85-6.85 Å). In MOF-monoclinic the extended

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“stack” SBU forming triangle pores with an edge length of ∼7 Å. The small kinetic 8 Page 8 of 52

diameter of p-Xylene (5.85 Å) resulting in the biggest diffusion coefficient on MOF-

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monoclinic and a preferable adsorption. The adsorption and separation of xylene

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isomers and EB were equilibrium controlled on MOF-5 and diffusion dominated on

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the monoclinic MOF. On the basis of the measured McReynolds constants [77],

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MOF-5 was characterised as a nonpolar stationary phase, whereas the monoclinic

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MOF was characterised as an intermediate polarity phase for gas chromatography.

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Another study by Scott et al. showed that MOF-199 or HKUST-1 [Cu3(BTC)2)]

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packed columns provided selective retention of small Lewis-base organic analytes

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(Figure 3) [78]. MOF-199 was chosen as the MOF material for this study because it

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was relatively easy to prepare, displayed an intermediate Lewis acidity and the pore

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size was appropriate for many small organic analytes. The study examined MOF-199

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when loaded in stainless steel columns prepared from tubing cut to dimensions of

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1.83-2.74 m × 3.18 mm od (2.1 mm id) at various concentrations (5.0, 0.75 and

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0.10%, w/w) on an inert support material (Chromosorb W HP) that had been

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deactivated with a low loading of a non-polar stationary phase (3% SE-30). The

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results showed that the MOF-199-containing stationary phase had limited thermal

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stability (220°C) and a strong general retention for analytes. The Kováts index

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calculations showed selective retention relative to n-alkanes for many small Lewis-

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base analytes on a column that contained 0.75% Cu-BTC compared with an SE-30

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control.

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Borjigin et al. presented a 2D microporous MOF JUC-110 [Cd(H-thipc)2.6H2O] (thipc; (S)-4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylate), with 1D hydrophilic channels of approximately 4.5 Å × 4.5 Å for GC separation [79]. The packed-column (180 mm long × 2 mm i.d.) was filled with samples of JUC-110 and utilised for the separation of alcohol-water mixtures. The GC separation showed that the ethanol and methanol can be separated from water with retention times of 0.36

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min, 15.89 min and 8.84 min respectively. JUC-110 square channels excluded

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alcohols larger than and equals to 4.5 Å but accommodated smaller molecules

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including water and methanol. Because the size of methanol molecules fits better with

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the channels of JUC-110 than water molecules, water moves faster than methanol.

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JUC-110 exhibits exceptional hydrothermal stability; even under treatment with

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boiling water for ten days, it retains its crystalline structure, which is rare among 9 Page 9 of 52

porous MOFs, especially 2D ones [79]. The low hydro-stabilty of MOFs is a feature

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that not fully understood until now. In the case of hydrophilic MOFs, the water binds

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to unsaturated metal sites, leading to structural changes and framework’s collapse.

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While in hydrophobic MOFs, the metal containing SBU clusters act as “weak

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hydrophilic defects”. A water cluster could fully displace one arm of a linker and

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which means the loss of the material’s ordered structure [80].

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showed poor thermal stability (≈200°C).

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The UiO-66 structure was developed by Cavka et al. [81]. The structure of this MOF

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is composed of a zirconium inorganic brick [Zr6O4 (OH)4(CO2)12] linked with twelve

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terephthalate ligands (BDC). Bozbiyik et al. demonstrated the inverse shape-selective

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behaviour of UiO-66 in the adsorption and separation of linear and cyclic alkanes

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through a packed column [84]. Stainless steel chromatographic columns (300 mm

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long × 3.12 mm i.d.) filled with 500 mg pellets (UiO-66) with sizes of 530–600 μm

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were used. They found that cyclohexane fits better in the pores of UiO-66, leading to

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a more negative adsorption enthalpy and a decreased loss of entropy during

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adsorption compared to n-hexane. The cyclic molecule loses less freedom in the

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interwoven structure of small (~8 Å) and large (11 Å) pores in UiO-66 compared to

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the linear n-hexane molecule.

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The physicochemical properties of MOF-5 were determined using inverse gas

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chromatography (IGC) by Luebbers et al. [83]. They utilised micropacked capillary

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columns to investigate the effect of structural degradation upon volatile organic compounds (VOCs) adsorption using more than 30 VOCs on MOF-5. MOF-5, which has a surface area of ≈1000 m2.g-1, is characterised by cages that are approximately 15 Å across and connected by pore openings of approximately 7.5 Å. The results indicated that the samples of MOF-5 experienced a moderate amount of structural degradation showed a stronger interaction with adsorbed species than MOF-5 with

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fewer defects, resulting in higher heats of adsorption These results show that the

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mechanisms of interaction of VOCs with MOFs is more complicated and further work

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is needed to make that process more clear.

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Another IGC study was performed to determine the adsorption behaviours of VOCs

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on three isoreticular metal-organic frameworks (IRMOFs) [84]. For this purpose,

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Gutiérrez et al. selected three samples of IRMOFs as adsorbents (IRMOF-1, IRMOF10 Page 10 of 52

8 and IRMOF-10) and different types of volatile organic compounds (VOCs) as

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adsorbates. It was found that the adsorption capacity at infinite dilution and the

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enthalpy of adsorption increased with the cavity diameter of the structures. As a

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general trend, it was observed that the strength of the interaction increases in the order

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IRMOF-1 < IRMOF-8 < IRMOF-10 because of the presence of lattice defects, such as

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metal clusters in the pores, lattice interpenetration, or the increase in the number of

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carbon atoms of the organic linkers. It was also observed that the specificity of the

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interactions is related to the chemistry of the organic linkers more than the structure of

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the IRMOFs because the presence of π-electron rich zones (aromatic rings or double

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bonds) enhanced the specificity of the interaction by the favoured interaction with the

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aromatic rings of the organic linker molecules.

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3.1.2 Open-tube capillary columns

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The first MOF-coated open-tube capillary column for GC separation was reported in

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2010 by Gu and Yan [85]. MIL-101[Cr3O(H2O)2F(BDC)3] was used as the stationary

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phase, and xylene isomers and ethylbenzene (EB) were used as the targets for

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separation. MIL-101 was chosen as the stationary phase because of its large surface

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area of 5900 m2.g-1, unusually large pores (29 and 34 Å), and excellent chemical and

331

thermal stability [86]. The fabricated capillary column was (15 m long × 0.53 mm

332

i.d.), and the MIL-101 films coated on the inner walls of the capillary column had a

333

thickness of approximately 0.4 mm. Only 1 mg of MIL-101 was needed for the

335 336 337 338 339

cr

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an

M

d

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Ac ce p

334

ip t

314

fabrication of a capillary column, which is one advantage for capillary columns over packed columns. The MIL-101-coated capillary column showed efficient baseline separation of xylene isomers and ethylbenzene within 1.6 min and with 3800 plates.m1

for p-xylene (Figure 4). The excellent and efficient separation using MIL-101-coated

capillary columns was due to host-guest interactions, accessible open metal sites (coordinatively unsaturated sites CUSs) and suitable polarity of MIL-101.

340

ZIF-8 [Zn(2-methylimidazole)2] has been explored by Chang et al. as a molecular

341

sieving material [87]. The molecular sieving effect is known as the preferential

342

adsorption of molecules with smaller kinetic diameters than the bulkier ones in the

343

micropores [88]. The large pores (11.4 Å) of ZIF-8 along with the 3.4 Å pore

344

openings were found to have the ability to separate linear alkanes from branched

345

alkanes in coated capillary columns. The molecular sieving effect of ZIF-8 led to the 11 Page 11 of 52

separation of branched alkanes from linear alkanes; however, the branched isomers

347

were not completely separated from each other (Figure 5). The same research group

348

produced an elegant combination of ZIF-8-coated fibres for solid phase micro-

349

extraction (SPME) using a ZIF-8-coated capillary for subsequent GC separation [89].

350

They demonstrated a MOF-based tandem molecular sieve platform for the selective

351

microextraction of n-alkanes and high-resolution GC separation in complex

352

petroleum-based fuels and human serum samples. A combination of a ZIF-7

353

[Zn(benzimidazolate)2]-coated SPME fibre with a MIL-101 [Cr3O(H2O)2F(BDC)3]-

354

coated capillary GC has also been examined, revealing the ability to selectively

355

extract benzene homologues and the high-resolution separation of substituted benzene

356

derivatives [89]. This dual-platform combination provides new possibilities for real

357

sample analysis because of the large diversity of MOF structures.

358

Another molecular sieving material has been tested for coated capillary columns in

359

GC separations. Chang and Yan estimated the reverse-shape selectivity of the

360

molecular sieving MOF material UIO-66 with BDC as the organic linker [88]. UIO-

361

66 has cubic, rigid, 3D-pore structure consisting of octahedral cavities with diameters

362

of 11 Å and tetrahedral cavities with diameters of 8 Å. The accessibility of the

363

cavities is ensured by the microporous triangular windows with diameters in the range

364

of 5–7 Å, which is close to the critical diameter of alkanes and benzene homologues.

365

It was found that a UiO-66-coated capillary column affords stronger retention for

366

372

Ac ce p

373

iso-propylbenzene. This result is due to the narrow pore window of UIO-66, which

374

prevents the bulkier 1,3,5-trimethylbenzene from passing into the micropores.

375

The effect of the metal ion in isostructural MOFs on the chromatographic separation

376

has been investigated by Fan and Yan [91]. The isostructural metal-organic

377

frameworks

367 368 369 370 371

te

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346

branched alkanes than their linear isomers (Figure 6). The reverse-shape selectivity of UIO-66 was related to the stronger van der Waals interactions between the side methyl groups on the alkane chains and the pore walls. Additionally, the differences in the polarisabilities of the C–H groups of the branched alkanes could vary the direct dipole-induced hydrogen bonding between the acid sites of UiO-66 and the alkanes, resulting

in

reverse-shape

selectivity

[90].

However,

the

bulkier

1,3,5-

trimethylbenzene appeared to elute earlier than the less bulky n-propylbenzene and

MIL-100(Fe)

[(Fe3OF3(BDC)3).

nH2O]

and

MIL-100(Cr) 12 Page 12 of 52

[(Cr3OF3(BDC)3). nH2O], which have identical organic linkers but different metal

379

ions, were used as the stationary phases in the capillary gas chromatographic

380

separation of alkane isomers. The MIL-100(Fe)-coated columns offered excellent

381

features for capillary gas chromatographic separation of alkane isomers with excellent

382

reproducibility, even better than commercial capillary columns, whereas the MIL-

383

100(Cr)-coated capillary column produced poor separation (Figure 7). The

384

McReynolds constants were used to describe the polarities of the MIL-100 columns.

385

The larger McReynolds constants of the MIL-100(Cr)-coated column indicate that

386

MIL-100(Cr) shows a stronger hydrogen bonding ability than MIL-100(Fe).

387

Moreover, According to the molecular simulation studies by Nicholson and Bhatia

388

[92], Fe(III) has a smaller radius and stronger electrostatic Coulomb interaction with

389

the oxygen in the framework than Cr(III). Therefore, MIL-100(Fe) donates less partial

390

negative charge to the framework oxygen, which in turn weakens the C–H…O bonds

391

between the CH groups of the alkanes and the framework oxygen atoms compared

392

with MIL-100(Cr).

393

The dynamic coating method [93, 94] is the primary method for preparing capillary

394

columns coated with MOFs for GC separations. This procedure is performed by

395

slowly flushing slurries of these materials through fused silica capillaries. The MOF-

396

coated capillaries, using dynamic coating technique, come closest to the ideal porous

397

layer open tubular (PLOT) columns, although they possess significantly larger pore

398

404

Ac ce p

405

method based on the so-called “controlled SBU-approach” (CSA) for MOF-5 [95] and

406

MOF-199 [97]. This technique forms a thin MOF layer through bonding of the MOF

407

to the substrate surface via a self-assembled monolayer (SAM). The preparation of a

408

SAM provides a layer that serves as an adhesive primer and allows for the growth of

409

the MOF components (after a layer of SBUs) on the fused silica of standard

410

chromatographic capillaries [95]. The exchange reaction between the monotopic

399 400 401 402 403

te

d

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cr

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378

sizes than MOFs. However, the major disadvantage of these coatings is the column bleeding due to spiking, which is the detachment of small particles from the coatings over time that appears as spikes in the chromatograms if a particle filter is not used [95]. Crosslinking of the stationary phase material and chemical bonding of the coatings to the column overcome the bleeding problem. Columns of this type are commercially labelled as “bonded PLOT columns” [96]. Likewise, another technique reported by Münch et al. to prepare MOF-coated capillaries is the cyclic deposition

13 Page 13 of 52

ligands of the SBU precursor and the multitopic linkers leads to interconnection of the

412

SBUs to form the 3D network structure [98].

413

The MOF-CSA column is mainly used for the analysis of permanent gases and low-

414

molecular-weight hydrocarbons. MOF-5-CSA and MOF-199-CSA columns were

415

used for natural gas separations [95, 97]. The performance of the MOF-5-CSA

416

column was equivalent, if not superior, to the leading technology for analytical natural

417

gas separation (Figure 8); it displayed great stability over five months, performing

418

more than 300 chromatographic separations (in the range 40–150°C) without any

419

significant loss of separation power [95]. Conversely, the MOF-199-CSA column

420

presented a less suitable separation of natural gas than a similar MOF-5-CSA column

421

[97]. Böhle and Mertens also use the same technique to prepare DMOF-1

422

[Cu2(BDC)2(DABCO)] (DABCO; 1,4-diazabicyclo(2,2,2)octane)-coated capillary for

423

the GC separation of light hydrocarbons [99]. They used a layer-by-layer deposition

424

technique developed by Fischer et al. [100] and Wöll et al. [101] to enable the

425

preparation of non-interpenetrating large pore DMOF-1-type frameworks on various

426

surfaces. The fabricated column (10 m long × 0.53 mm i.d.) exhibits high separation

427

power for the light hydrocarbons C1-C7. The cyclic CSA method for the preparation of

428

MOF-coated capillaries may add new features, such as controlled growth on the

429

molecular scale or the possibility of creating heterostructures [97].

430

MOF-CJ3 [(HZn3(OH)(BTC)2(2H2O) (DMF)). H2O] [102] was selected as a gas

432 433 434 435 436

cr

us

an

M

d

te

Ac ce p

431

ip t

411

chromatography stationary phase by Fang et al. [103]. MOF-CJ3 possesses extended 1D tubular channels. Its pore wall is composed of BTC ligands, which can provide benzene rings and carboxyl groups to form supramolecular interactions. A relatively short column (10 m long × 0.32 mm i.d.) has been used to separate various types of hydrocarbons, such as linear and branched alkanes, xylene isomers, EB, and aromatic positional isomers (Figure 9). The theoretical plate numbers obtained from substituted

437

aromatic compounds are in the 361 to 1466 plates.m-1 range for this GC column,

438

which is lower than other MOF-based capillary columns. The 1D tubular pores of

439

MOF-CJ3 possess dimensions of 11.6 Å × 11.6 Å, which are accessible to both linear

440

and branched alkanes; therefore, the retention of alkanes on this column depends

441

mainly on the van der Waals forces between the analyte molecules and the MOF

442

materials [103]. 14 Page 14 of 52

3.2 High-performance liquid chromatography applications

444

Although high-performance liquid chromatography (HPLC) remains the least

445

common chromatographic application for MOFs, it represents an area in which

446

continuing research may reveal many new and superior stationary phases for HPLC.

447

Several MOFs have been studied for HPLC applications [104, 112-120]. However,

448

there are many types of MOFs that have not yet been studied for HPLC. The

449

application of MOFs in HPLC, including normal and reverse phase, also requires

450

examining single or binary mobile phases.

451

MIL-47(V) [VIVO(BDC)] and MIL-53(Al) [AlIII(OH)(BDC)] were the first MOF

452

materials to be used in LC applications by Alaerts and co-workers [104]. The pore

453

architectures of these materials are similar (one-dimensional pores), and they were

454

fully characterised by Férey and co-workers, who revealed a novel series of MOFs

455

with new topologies [105- 111]. MIL-47 has a pore volume of 0.32 cm3.g-1 and a

456

surface area of 750 m2.g-1, whereas MIL-53 has a pore volume of 0.50 cm3.g-1 and a

457

surface area of 940 m2.g-1 [112]. The main difference between MIL-47 and MIL-53 is

458

the presence of OH vertices in MIL-53, resulting in a highly flexible character, while

459

MIL-47 does not contain OH groups, which makes it more rigid [112].

460

First, the competitive adsorption equilibria of liquid mixtures of EB and xylene

461

isomers in hexane were studied. MIL-47 preferred p-xylene over m-xylene with a

462

selectivity of 2.9:1, whereas MIL-53(Al) hardly distinguished between these isomers

468

Ac ce p

te

d

M

an

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cr

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443

469

that p-xylene is packed more easily inside the MIL-47 pores than m-xylene or EB

470

[104].

471

The same research group continued their work on MIL-47 and MIL-53. They

472

performed an interesting comparison on the adsorption of alkylaromatics on both

473

materials [112, 113]. On MIL-47, o- and p-ethyltoluene are almost equally preferred

474

and are more strongly retained than m-ethyltoluene (Figure 11-a). Improved

463 464 465 466 467

[104]. In a breakthrough pulse chromatographic experiment, a ternary mixture of EB, m-xylene, and p-xylene was injected into an MIL-47-packed column in a normal phase system with hexane as the desorbent flowing at 4 ml.min-1 through the column. Three well-separated peaks were obtained in the chromatogram (Figure 10). The selectivities were 9.7:1 for p-xylene vs. EB and 3.1:1 for p-xylene vs. m-xylene. The isotherms for p-xylene and o-xylene reached a plateau of 35–37 wt%, which shows

15 Page 15 of 52

separation occurs at higher alkylaromatic concentrations. Conversely, MIL-53(Al)

476

possessed different selectivity patterns; the o-isomer elutes later than the other

477

isomers, which are not separated from each other (Figure 11-b) [113]. The different

478

interaction strengths were responsible for this order of selectivity. They also

479

suggested that MIL-47 selectively adsorbs the p-isomer from para–meta mixtures of

480

disubstituted aromatics, such as ethyltoluenes, xylenes, dichlorobenzenes, toluidines

481

and cresols. This preference in adsorption was found to be dependent on the external

482

concentration, which subsequently depends on the functional groups, molecular

483

packing, stearic hindrance and hydrogen bonding [112].

484

The adsorption selectivities for mono- and di-substituted alkylaromatics with various

485

alkyl groups in MIL-47 and MIL-53 were investigated by determining the adsorption

486

enthalpies at low or high loading using either pulse chromatographic or calorimetric

487

methods [114]. It was found that the separation of cumene (isopropylbenzene) and n-

488

propylbenzene on MIL-47 is an enthalpy-based separation because the uptake of

489

cumene on MIL-47 is enthalpically less favoured than that of n-propylbenzene due to

490

the presence of a branched isopropyl group. Furthermore, as the length of the alkyl

491

chain of n-alkylbenzenes increased, the adsorption enthalpy also increased. While the

492

preferential adsorption of xylenes over EB on MIL-47 was found to be controlled via

493

entropic effects, the preference for xylenes over EB in MIL-53 was due to enthalpic

494

effects [114].

496 497 498 499 500

cr

us

an

M

d

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Ac ce p

495

ip t

475

De Malsche et al. reported that the separation of EB, p-xylene and o-xylene using a glass capillary column (11.6 cm long × 0.15 mm i.d.) packed with MIL-53(Al) showed an unusual pressure drop when the temperature was increased (Figure 12) [115]. These drops are attributed to the breathing effect of the flexible MIL-53(Al) structure. The degree of expansion of MIL-53(Al) as a function of temperature could be useful for pressure-controlled separations. Moreover, this behaviour could provide

501

a successful method for faster separations at higher temperatures without influencing

502

the selectivity.

503 504

Yan and co-workers made a significant development in the liquid chromatographic

505

applications of MIL-47 and MIL-53. They explored the use of a binary mobile phase

506

with a MIL-53(Al)-packed column for HPLC separations. The utilisation of a 16 Page 16 of 52

507

hexane/dichloromethane or dichloromethane/methanol binary mobile phase provided

508

high-resolution

509

nitrophenol isomers [116]. The baseline separations were achieved with 10200

510

plates.m-1 column efficiency for EB and a high resolution. Moreover, the first reverse-

511

phase separation on HPLC (RP-HPLC) using MOF materials was also reported by the

512

same group [117]. High-resolution separations of a wide range of analytes, from non-

513

polar to polar and acidic to basic solutes, were achieved using stainless-steel columns

514

(7 cm long × 4.6 mm i.d.) packed with MIL-53(Al) and CH3CN/H2O as the mobile

515

phase. The separations depended on the combined mechanisms of size-exclusion,

516

shape selectivity and hydrophobicity [117].

517

MIL-101 is another MOF material that has been used for HPLC separations. A MIL-

518

101 packed column (5 cm long × 4.6 mm i.d.) in combination with CH2Cl2/CH2CN

519

(98:2) as the mobile phase has been utilised for the separation of fullerenes [118]. A

520

high-resolution, rapid separation of C60 and C70 was achieved within 3 min with

521

superior selectivity (R(C70/C60) = 17) and a high column efficiency of 13000

522

plates.m-1 for C70. The MIL-101-packed column was also examined for the separation

523

of the higher fullerenes (C76, C78, C82, C84, C86, and C96) (figure 13). It was concluded

524

that the exceptional selectivity of MIL-101 for fullerenes results from several factors,

525

including the difference in the solubility of fullerenes in the mobile phase, diffusion

526

through the pores of MIL-101, and π-π and van der Waals interactions between the

527

533

Ac ce p

534

good precision and excellent reproducibility. However, relatively low column

535

efficiency was observed (11262 plates.m-1 for o-chloroaniline) for the lab-made MIL-

536

100(Fe) packed column due to the irregular particle shapes. The mobile phase

537

composition had a significant effect on both the RP-HPLC and NP-HPLC separations.

538

The thermodynamic study of the MIL-100(Fe) column indicated an exothermic RP-

539

HPLC separation and an endothermic NP-HPLC separation. The selectivity changed

528 529 530 531 532

of

xylene,

dichlorobenzene,

chlorotoluene,

and

te

d

M

an

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cr

ip t

separations

fullerenes and the inner walls of the pores of MIL-101 [118]. Recently, MIL-100(Fe) [(Fe3OF3(BDC)3). nH2O] was explored by Yan’s group as a stationary phase for both normal-phase (NP) and reverse-phase (RP) HPLC [119]. In the RP-mode, two groups of neutral and basic analytes were used to test the separation performance of MIL-100(Fe), whereas chloroaniline and toluidine isomers were used for the NP-mode (Figure 14). Baseline separation of all analytes was obtained with

17 Page 17 of 52

significantly with the temperature, indicating the capacity for temperature-dependent

541

separations on MIL-100(Fe)-packed column. The negative ΔG values indicated a

542

spontaneous transfer of all analytes from the mobile phase to the stationary phase. The

543

MIL-100(Fe) MOF material was found to be a successful candidate for both RP and

544

NP-HPLC separations based on the π-π, hydrogen bond and coordination interactions,

545

which resulted from the presence of the aromatic rings, the carboxyl groups and the

546

metal active sites [119].

547

The irregular shape of MOFs and the size variations lead to lower column efficiency

548

of such MOF-packed columns for HPLC applications. The fabrication of

549

monodisperse MOF@SiO2 core-shell microspheres as the stationary phase for HPLC

550

was proposed to solve this problem [120]. 400 nm ZIF-8 shell was grown on a

551

carboxyl modified 3.0 μm silica spheres support after three cycles of ZIF-8 growth.

552

No significant increase of ZIF-8 density was noticed with increasing number of

553

growth cycles. The fabricated ZIF-8@SiO2 core-shell possess a BET surface area of

554

565.3 m2.g-1, and a total pore volume of 0.48 cm3.g-1. A packed columns (5 cm long ×

555

4.6 mm i.d.) with the monodisperse ZIF-8@SiO2 show a very low column

556

backpressure of 10 bar, and a high efficiency within 7 min for the HPLC separation of

557

endocrine disrupting chemicals (EDCs) and pesticides (23000 plates.m-1 for bisphenol

558

A). The high ratio of water (10%, v/v) within the mobile phase significantly decreased

559

the resolution of the EDCs or pesticides separation. The ZIF-8@SiO2 monodisperse

560

Ac ce p

561 562 563 564 565

te

d

M

an

us

cr

ip t

540

microspheres overcomes the main disadvantage that limits the usage of MOFs as stationary phase for HPLC separation and open up a new field for MOFs application in liquid chromatography [120]. 3.3 Other chromatographic applications In a proof-of-concept experiment, Han et al. demonstrated that chromatographic separations could be performed in a single MOF crystal [121]. They used single

566

MOF-5 crystals with millimetre-sizes (from approximately 1 × 1 × 1 mm to 3 × 3 × 2

567

mm) as the chromatographic column. The separation of organic dye mixtures was

568

detected using fluorescence confocal microscopy over a distance of only a few

569

hundred micrometres. Dimethylformamide (DMF) was used as the mobile phase

570

because it has no effect on the integrity of the MOF-5 crystal, while other solvents,

571

such as H2O, CH3CN, MeOH, CH2Cl2, and THF, resulted in crystal cracking. 18 Page 18 of 52

Moreover, the MOF crystal can be reused after simply soaking in fresh DMF for 24 h.

573

A future study on single MOF crystal chromatographic separations will be a great

574

accomplishment in the enormous challenge of miniaturisation in chromatography.

575

Li et al. utilised MOFs for capillary electrokinetic chromatography (EKC) for the first

576

time [122]. EKC is a relatively new chromatographic technique based on a

577

combination of the high efficiency of capillary electrophoresis (CE) and the

578

selectivity of HPLC [123]. They found that ZIF-8 met the requirements for the

579

pseudostationary phase (PSP) in EKC. A baseline separation of six phenolic isomers

580

within only 4 min was observed with more than 85000 plates.m-1 (except for p-

581

benzenediol). The unique 3D porous frameworks with a large surface area found in

582

ZIF-8 led to strong interactions between the phenolic hydroxyl groups of the solutes

583

and ZIF- 8, which yielded good separation.

584

Capillary electrochromatography (CEC) is one of the most recent chromatographic

585

techniques to use MOF materials as stationary phases. Xu et al. reported an in situ,

586

self-assembly, layer-by-layer method for fabricating MIL-100(Fe)-coated open-

587

tubular capillary columns for CEC [124]. They proposed a new technique to control

588

the capillary coating with MOF materials. GLYMO-IDA-silane was synthesised

589

through the reaction between 3-glycidoxypropyltrimethoxysilane (GLYMO) and

590

iminodiacetic acid (IDA) according to Zou et al. [125] and attached to the inner walls

591

of the capillaries after etching and chemical modification. FeCl3·6H2O was then

593 594 595 596 597

cr

us

an

M

d

te

Ac ce p

592

ip t

572

pumped into the capillary, followed by a BTC ethanol solution, to form the first cycle of MIL-100(Fe). Repeating the last step led to a series of open-tubular capillary columns with varying layers of MIL-100(Fe). Neutral, acidic and basic analytes were successfully separated with very good selectivity and excellent reproducibility using a 10-cycle MIL-100(Fe) column. The suitability of MIL-100(Fe)-coated open-tubular capillary columns for different types of analytes was due to the hydrophobicity of the

598

organic ligands and the size selectivity of the lattice aperture. Moreover, the

599

absorbance and quantity of MIL-100(Fe) were found to be proportional to the number

600

of coating cycles.

601

Metal-organic framework materials in composite polymers are another interesting

602

application in CEC. The incorporation of MOF CAU-1 [(Al8(OH)4-(OCH3)8(BDC-

603

NH2)6)] into polymethyl methacrylate (PMMA) to produce CAU-1@PMMA 19 Page 19 of 52

composite was reported for coated open-tubular CEC applications [126]. The solution

605

of CAU-1 and the polymerisation mixture in DMSO was simply passed through a

606

capillary (30 cm long × 0.075 mm i.d.), leaving a thin layer of the solution on the

607

inner wall, which was subsequently thermally polymerised to produce a very rough

608

inner surface. No baseline separations of the selected aromatic acids and nonsteroidal

609

anti-inflammatory drugs were observed on a MOF-free column. However, the

610

composite-coated capillary (CAU-1@PMMA column) achieved a higher efficiency

611

(16964 plates.m-1 for ketoprofen and 66327 plates.m-1 for benzoic acid), shorter

612

separation time, increased loading capacity for the separation of aromatic acidic

613

compounds and improved resolution of the tested drugs.

614

Open-tubular capillary columns are not the exclusive form of MOF stationary phases

615

for CEC. MIL-101(Cr) incorporated into a methacrylate polymer (PMA) monolith

616

was developed for CEC and nano-liquid chromatography (nano-LC) [127]. A neat

617

polymer column and a MIL-101(Cr)-packed column were prepared using the same

618

conditions for comparison. Microwave-assisted polymerisation was used to prepare

619

the columns in only 5 min. Efficient separations were achieved for a group of various

620

aromatic compounds (Figure 15), polycyclic aromatic hydrocarbons (PAHs) and

621

trypsin-digested BSA peptides using a MIL-101(Cr)@PMA monolithic capillary

622

column. The incorporation of the MIL-101(Cr) MOF provided a much larger surface

623

area than the neat polymer and also provided the stationary phase with meso- and

624

Ac ce p

625 626 627 628 629

te

d

M

an

us

cr

ip t

604

nano-pores In addition, this hybrid MOF–polymer column possessed high permeability compared to the MOF-packed column, with an approximately 800-fold increase.

UiO-66 incorporated PMA monoliths were successfully used to enhance the HPLC separation of small molecules with high column efficiency and good reproducibility [128]. A stainless-steel column (7 cm long × 4.6 mm i.d.) filled with UIO-66@PMA

630

monolith composite with an average particle size of 210 nm of UIO-66 was utilized to

631

enhance HPLC separation of neutral polycyclic aromatic hydrocarbons, basic aniline

632

series, acid phenol series, and naphthyl substitutes. The prepared column showed an

633

increase in BET surface area (321.4 m2.g-1) as compared to a similar monolithic

634

column without UIO-66 (192.6 m2.g-1). Using different concentrations of UiO-66

635

showed an increase in the retention of the small molecules and their resolutions with 20 Page 20 of 52

the increased amount of the UiO-66 incorporated. The retention and resolution of all

637

of the analytes decreased with increasing the content of ACN in the mobile phase.

638

UIO-66@PMA monolithc column offered a column efficiency of 28800 plates.m-1 for

639

2, 6-dimethylphenol, while monolith without incorporating UiO-66 gave a poor

640

column efficiency (2967-8218 plates.m-1). The enhanced separation performance of

641

UiO-66 incorporated PMA monoliths for small molecules mainly resulted from the π-

642

π interaction, the hydrophobic interaction and the interaction between the nitrogen

643

atom in the analyte and the Zr active sites in UiO-66 [128].

644

The separation of racemic mixtures using enantioselective stationary phases is often

645

required. However, it always been a complicated and expensive process. Homochiral

646

metal-organic frameworks (HMOFs) are a new family of MOFs that can serve as

647

Chiral Stationary Phases (CSPs). HMOFs are usually synthesized by using chiral

648

linkers with a metal containing node. Molecular modeling simulations were used by

649

Bao et al. to screen 8 HMOFs for their ability to separate 19 chiral compounds by

650

enantioselective adsorption [129]. They have noticed that there is a lack of correlation

651

between the enantioselectivities of a homologous series of chiral compounds. The

652

shift in the adsorption site was the mean reason for the uncorrelated

653

enantioselectivities, which could be preserved by a smooth HMOF pore [129]. It was

654

demonstrated that there is a strong correlation between the size of the pore and the

655

size of the chiral analyte [130]. Size matching between the chiral HMOF stationary

656

Ac ce p

657 658 659 660 661

te

d

M

an

us

cr

ip t

636

phase and the chiral molecule led to the formation of a tight inclusion complex which increases the enantioselectivity. However, even with size matching exists between the size of the pore and the size of the chiral molecule no enantioselectivities were obtained. Using a slightly different size chiral selector was suggested to solve that problem [130].

Yuan’s group employed several D-Cam (D-camphoric acid) based HMOFs as

662

homochiral stationary phases [131-133]. High-resolution gas chromatographic

663

separation

664

trimethylenedipyridine)]-coated

665

Cam)1/2(BDC)1/2(tmdpy) structure possesses a 3-D framework with enantiopure

666

building blocks embedded in intrinsically chiral topological nets. They prepared two

667

fused-silica open tubular columns with different inner diameters and lengths,

was

performed

on

Co(D-Cam)1/2(BDC)1/2(tmdpy) open

tubular

columns

[131].

[tmdpy= The

4,4′Co(D-

21 Page 21 of 52

including column A (30 m long × 0.53 mm i.d.) and column B (2 m long × 0.075 mm

669

i.d.), by a dynamic coating method using Co-(D-Cam)1/2 (BDC)1/2 (tmdpy) as the

670

stationary phase. The number of theoretical plates of the two metal-organic

671

framework columns was 1450 and 3100 plates.m-1, respectively, using n-dodecane as

672

the test compound at 120 °C. The LOD (limit of detection) and LOQ (limit of

673

quantification) were found to be 0.125 and 0.417 ng for citronellal enantiomers,

674

respectively. A similar homochiral MOF (Ni(D-Cam)(H2O)2) was chosen as stationary

675

phase for high-resolution GC separation by the same research group [132]. The

676

experimental results of both stationary phases showed an excellent chiral recognition

677

ability toward racemates due to the chiral microenviroment with its unusual

678

integration of molecular chirality, 3-D intrinsic chiral net, and absolute helicity [131,

679

132].

680

[Cu2(D-Cam)2(4,4′-bpy)]n with 3-D six-connected self-penetrating architectures was

681

another D-Cam based MOF material used for chiral separation [133]. This study

682

explored some effects such as mobile phase composition, column temperature, and

683

analytes mass for separations using [Cu2(D-Cam)2(4,4′-bpy)]n homochiral MOF on

684

HPLC. A 4.0 g mass of the prepared material was filled into a stainless steel column

685

(25 cm long × 4.6 mm i.d.) and used for the separations of positional isomers and

686

chiral compounds. A variety of solutes were tested including alcohols, a diol, a

687

naphthol and a ketone racemates. The results proved that [Cu2(D-Cam)2(4,4′-bpy)]n

688

Ac ce p

689 690 691 692 693

te

d

M

an

us

cr

ip t

668

showed good selectivity for positional isomers and enantiomers. In thermodynamic terms, the negative values of ΔG indicated a spontaneous transfer of analytes from the mobile phase to the stationary phase. The interaction between solutes and the surface of homochiral layers or channels are possibly the main interactive force [133]. A successful chiral separation using Zn(ISN)2.2H2O [ISN= isonicotinic acid] with a large (~8.6 Å) left-handed channel was performed for high-resolution GC [134]. The

694

column efficiency of Zn(ISN)2.2H2O-coated column was up to 3020 plates.m-1. The

695

separation performance of a dynamic coated capillary column (3 m long × 0.075 mm

696

i.d.) was investigated through a wide range of organic compounds separation. The

697

results showed that Zn(ISN)2.2H2O stationary phase possesses high column

698

efficiency, good reproducibility, excellent selectivity, and chiral recognition ability.

699

4. Conclusions 22 Page 22 of 52

The utilisation of metal-organic frameworks in chromatography has witnessed

701

significant developments over the last five years, with progressive improvements year

702

after year. The unique properties of MOFs provide new properties for

703

chromatographic separations. We have reviewed the most significant and recent

704

advances in MOF applications for HPLC, GC, CEC, and other chromatographic

705

techniques. MOFs have been introduced as packed columns, open-tubular capillary

706

columns, monolithic columns and even as a single crystal column. The packed

707

columns showed excellent performance with significant stability for HPLC and GC.

708

However, the variability in the particle size and irregularity are the greatest

709

challenges. The monodisperse MOF@SiO2 core-shell microspheres as stationary

710

phase for HPLC has been proposed recently to overcome the irregularity and size

711

variations problem of MOF packed particales. Another problem accompanied with the

712

packed MOF columns is the high cost due to the need for large amounts of material

713

to fill the packed column. A number of thermodynamic studies using IGC were

714

performed seeking for a deeper under standing of the adsorption nature on MOF

715

materials. However, it needs more researches to get the complete picture.

716

The open-tubular capillary columns also produce very good results for GC and CEC

717

applications; in addition, they avoid the cost problem of MOF-packed columns. The

718

main disadvantages of open-tubular MOF capillary columns which fabricated via the

719

dynamic coating method is the leak of the material out of the column with time. The

720

Ac ce p

721 722 723 724 725 726

te

d

M

an

us

cr

ip t

700

SBU-controlled approach has emerged to solve the leakage problem in coated capillaries and to provide a well-controlled method for capillary coating. A successful separation on a single crystal of MOF-5 was performed as a proof-of-concept experiment. This experiment introduces a new horizon of miniaturisation. Chiral separation is one of the most important and promising MOF application in separation science. Homochiral metal-organic frameworks (HMOFs) are a new revolutionary MOF materials that can serve as Chiral Stationary Phases (CSPs). The

727

enatioselectivety of MOFs emerged from the usage of a chiral linker within the MOF

728

structure giving an infinite probabilities to produce HMOFs for chromatographic

729

separations.

730

MOF-based hybrid materials such as MOF combination with organic monolithic

731

polymers exhibit a very good performance. A composite column of MOF particales 23 Page 23 of 52

incorporated into a monolithic polymers showed both advantage of high permeability

733

of monolithic materials and the high surface area and high resolution of MOFs for

734

chromatographic separation. Such combinations extend the properties of MOFs to

735

include the advantages of the combined material and even exclude some

736

disadvantages of using MOFs as stationary phase.

737

The use of MOFs in chromatography has revealed some unexpected behaviours. For

738

example, an unusual pressure drop with increasing temperature was observed for a

739

MIL-53(Al)-packed column in HPLC. Additionally, reverse-shape selectivity was

740

observed with UIO-66 in GC applications.

741

Although many MOFs have already been examined for chromatographic separations,

742

there are a hundreds of MOF materials that have not been studied for separation

743

science. Furthermore, chromatography has not yet taken advantage of the controllable

744

structure of MOFs to construct new types of MOFs specially designed for specific

745

applications. The precise control of MOF shape, pore size, and chemical nature

746

through the intelligent choice of both the metals and ligands would provide

747

chromatographers unlimited possibilities for stationary phases. Post-synthetic

748

modification of MOFs by adding functional groups may also lead to flexible smart

749

columns that could alter their separation ability according to the analyte. We believe

750

that continued research into the use of MOFs in chromatographic separations will

751

expose many fortuitous and distinctive results.

756

Ac ce p

te

d

M

an

us

cr

ip t

732

757

[2] H. Gliemann, C. Wöll, mater. today 15 (2012) 110.

758

[3] G. Férey, From Zeolites to Porous MOF Materials – the 40th Anniversary of

759

International Zeolite Conference R. Xu, Z. Gao, J. Chen, W. Yan, 170 (2007) 66.

760

[4] E.A. Tomic, J. Appl. Polym. Sci. 9 (1965) 3745.

761

[5] C. Robl, Mat. Res. Bull. 27 (1992) 99.

762

[6] B.F. Hoskins, R. Robson, J. Am. Chem. Soc. 112 (1990) 1546.

752 753 754 755

Acknowledgments

The authors acknowledge the financial support of this work by King Saud University through National Plan for Science and Technology grant # NPST ADV 2120-02.

References

[1] H. Furukawa, K.E. Cordova, M. O’Keeffe, O.M. Yaghi, Science 341 (2013) 974.

24 Page 24 of 52

[7] D. Venketaraman, G.B. Gardner, S. Lee, J.S. Moore, J. Am. Chem. Soc. 117

764

(1995) 11600.

765

[8] D. Maspoch, D. Ruiz-Molina, K. Wurst, N. Domingo, M. Cavallini, F. Biscarini,

766

J. Tejada, C. Rovira, J. Veciana, Nature Mater. 2 (2003) 190.

767

[9] S.R. Batten, N.R. Champness, X.-M Chen, J. Garcia-Martinez, S. Kitagawa, L.

768

Öhrström, M. O’Keeffe, M.P. Suh, J. Reedijk, Cryst. Eng. Comm. 14 (2012) 3001.

769

[10] D.J. Tranchemontagne, J.L. Mendoza-Cortés, M. O’Keeffe, O.M. Yaghi, Chem.

770

Soc. Rev. 38 (2009) 1257.

771

[11] O.M. Yaghi, H. Li, J. Am. Chem. Soc. 117 (1995) 10401.

772

[12]

773

Sarjeant, R.Q. Snurr, S.T. Nguyen, A.Ö. Yazaydın, J.T. Hupp, J. Am. Chem. Soc. 134

774

(2012) 15016.

775

[13] J. Rocha, M.W. Anderson, Eur. J. Inorg. Chem. 2000 (2000) 801.

776

[14] C. Serre, F. Taulelle, G. Férey, Chem. Commun. (22) (2003) 2755.

777

[15] M.I. Khan, L.M. Meyer, R.C. Haushalter, A.L. Schweitzer, J. Zubieta, J.L. Dye,

778

Chem. Mater. 8 (1996) 43.

779

[16] M. Cavellec, J.M. Grenèche, D. Riou, G. Férey, Chem. Mater. 10 (1998) 2434.

780

[17] S. Natarajan, S. Neeraj, A. Choudhury, C.N.R. Rao, Inorg. Chem. 39

781

(2000)1426.

782

[18] N. Guillou, Q. Gao, M. Nogues, R.E. Morris, M. Hervieu, G. Férey, A.K.

783

Cheetham, C.R. Acad, Sci. Paris, Ser. II (1999) 387.

785 786 787 788 789 790

cr

Jeong, B.G.

Hauser, C.E.

us

Eryazici, N.C.

Wilmer, A.A.

te

d

M

an

Farha, I.

Ac ce p

784

O.K.

ip t

763

[19] P. Feng, X. Bu, G. Stucky, Science 278 (1997) 2080. [20] G. Férey, Chem. Soc. Rev. 37 (2008) 191 [21] D.-K Bucar, G.S. Papaefstathiou, T.D. Hamilton, Q.L. Chu, I.G. Georgiev, L.R. MacGillivray, Eur. J. Inorg. Chem. 29 (2007) 4559. [22] E.R. Parnham, R.E. Morris, Acc. Chem. Res. 40 (2007) 1005. [23] H. Deng, S.Grunder, K.E. Cordova, C. Valente, H. Furukawa, M. Hmadeh, F. Gándara, A.C. Whalley, Z. Liu, S. Asahina, H. Kazumori, M. O’Keeffe, O. Terasaki,

791

J.F. Stoddart, O.M. Yaghi, Science 336 (2012)1018.

792

[24] H. Furukawa, Y.B. Go, N. Ko, Y.K. Park, F.J. Uribe-Romo, J. Kim, M.

793

O’Keeffe, O.M. Yaghi, Inorg. Chem. 50 (2011) 9147.

794

[25] D.J. Tranchemontagne, Z. Ni, M. O’Keeffe, O.M. Yaghi, Angew. Chem. Int. Ed.

795

47 (2008) 5136.

796

[26] G.M. Whitesides, Science 295 (2002) 2418. 25 Page 25 of 52

[27] O.M. Yaghi, M. O’Keeffe, N.W. Ockwig, H.K. Chae, M. Eddaoudi, J. Kim,

798

Nature 423 (2003) 705.

799

[28] B. Moulton, M.J. Zaworotko, Chem. Rev. 101 (2001) 1629.

800

[29] A.J. Blake, N.R. Champness, P. Hubbertstey, W. Li, M.A. Withersby, M.

801

Schroder, Coord. Chem. Rev. 183 (1999) 117.

802

[30] L. Carlucci, G. Ciani, P. Macchi, D.M. Proserpio, Chem. Commun., (17) (1998)

803

1837.

804

[31] L. Carlucci, G. Ciani, D.M. Proserpio, S. Rizzato, J. Chem. Soc. Dalton Trans.

805

(2000) 3821.

806

[32] L. Carlucci, G. Ciani, D.M. Proserpio, S. Rizzato, Chem. Commun. (2001) 1198.

807

[33] O.R. Evans, W. Lin, Acc. Chem. Res. 35 (2002) 511.

808

[34] K. Biradha, Y. Hongo, M. Fujita, Angew. Chem. Int. Ed. 39 (2000) 3843.

809

[35] O.M. Yaghi, H. Li, T.L. Groy, Inorg. Chem. 36 (1997) 4292.

810

[36] O.M. Yaghi, H. Li, C. Davis, D. Richardson, T.L. Groy, Acc. Chem. Res. 31

811

(1998) 474.

812

[37] M. Eddaoudi, D.B. Moler, H. Li, B. Chen, T.M. Reineke, M. O'Keeffe, O.M.

813

Yaghi, Acc. Chem. Res. 34 (2001) 319.

814

[38] A. Stein, S.W. Keller, T.E. Mallouk, Science 259 (1993) 1558.

815

[39] E.J. Corey, Chem. Soc. Rev. 17 (1988) 111.

816

[40] N.W. Ockwig, O. Delgado-Friedrichs, M. O’Keeffe, O.M. Yaghi, Acc. Chem.

817

Res. 38 (2005) 176.

819 820 821 822 823 824

cr

us

an

M

d

te

Ac ce p

818

ip t

797

[41] M. O’Keeffe, M. Eddaoudi, H. Li, T. Reineke, O.M. Yaghi, J. Solid State Chem. 152 (2000) 3.

[42] L. Pauling, J. Am. Chem. Soc. 51 (1929) 1010. [43] O. Delgado-Friedrichs, M. O’Keeffe, J. Solid State Chem. 178 (2005) 2480. [44] C. Baerlocher, W.M. Meier, D.H. Olson, Atlas of Zeolite Framework Types, Elsevier, Amsterdam, 5th revised ed., 2001. [45] M. O’Keeffe, M.A. Peskov, S.J. Ramsden, O.M. Yaghi. Acc. Chem. Res. 41

825

(2008) 1782.

826

[46] O. Delgado-Friedrichs, M. O’Keeffe, O.M. Yaghi. Phys. Chem. Chem. Phys. 9

827

(2007) 1035.

828

[47] H. Li, M. Eddaoudi, T.L. Groy, O.M. Yaghi, J. Am. Chem. Soc. 120 (1998)

829

8571.

830

[48] H. Li, M. Eddaoudi, M. O’Keeffe, O.M. Yaghi, Nature 402 (1999) 276. 26 Page 26 of 52

[49] H. Furukawa, O.M. Yaghi, J. Am. Chem. Soc. 131 (2009) 8875.

832

[50] P.J. Fagan, M.D. Ward, Sci. Am. 267 (1992) 48.

833

[51] M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O’Keeffe, O.M. Yaghi.

834

Science 295 (2002) 469.

835

[52] H.K. Chae, D.Y. Siberio-Pérez, J. Kim, Y.B. Go, M. Eddaoudi, A.J. Matzger, M.

836

O’Keeffe O.M. Yaghi, Nature 427 (2004) 523.

837

[53] H. Furukawa, N. Ko, Y.B. Go, N. Aratani, S.B. Choi, E. Choi, A.O. Yazaydin,

838

R.Q Snurr, M. O'Keeffe, Science 329 (2010) 424.

839

[54] S.S.-Y. Chui, S.M.-F. Lo, J.P.H. Charmant, A.G. Orpen, I.D. Williams, Science

840

283 (1999) 1148.

841

[55] X.-S. Wang, S. Ma, D. Sun, S. Parkin, H.-C. Zhou, J. Am. Chem. Soc. 128

842

(2006) 16474.

843

[56] D. Sun, S. Ma, Y. Ke, D.J. Collins, H.-C. Zhou, J. Am. Chem. Soc. 128 (2006)

844

3896.

845

[57] S. Ma, D. Sun, M. Ambrogio, J.A. Fillinger, S. Parkin, H-C Zhou, J. Am. Chem.

846

Soc. 129 (2007) 1858.

847

[58] X.-S. Wang, S. Ma, D. Yuan, J.W Yoon, Y.K. Hwang, J.-S. Chang, X. Wang,

848

M.R. Jørgensen, Y.-S. Chen, H.-C. Zhou, Inorg. Chem. 48 (2009) 7519.

849

[59] J. Lu, A. Mondal, B. Moulton, M.J. Zaworotko, Angew. Chem. Int. Ed. 40

850

(2001) 2113.

851

[60] L. Xie, S. Liu, C. Gao, R. Cao, J. Cao, C. Sun, Z. Su, Inorg. Chem. 46 (2007)

853 854 855 856 857 858

cr

us

an

M

d

te

Ac ce p

852

ip t

831

7782.

[61] M. Kramer, U. Schwarz, S. Kaskel, J. Mater. Chem. 16 (2006) 2245. [62] L.J. Murray, M. Dinca, J. Yano, S. Chavan, S. Bordiga, C.M. Brown, J.R. Long, J. Am. Chem. Soc. 132 (2010) 7856. [63] O. Kozachuk, K. Yusenko, H. Noei, Y. Wang, S. Walleck, T. Glaserc, R.A. Fischer, Chem. Commun. 47 (2011) 8509. [64] J.L.C. Rowsell, E.C. Spencer, J. Eckert, J.A.K. Howard, O.M. Yaghi, Science

859

309 (2005) 1350.

860

[65] O.K. Farha, C.E. Wilmer, I. Eryazici, B.G. Hauser, P.A. Parilla, K. O’Neill, A.A.

861

Sarjeant, S.T. Nguyen, R.Q. Snurr, J.T. Hupp, J. Am. Chem. Soc. 134 (2012) 9860.

862

[66] S. Brunauer, P.H. Emmett, E. Teller, J. Am. Chem. Soc. 60 (1938) 309.

863

[67] J. Moellmer, E.B. Celer, R. Luebke, A.J. Cairns, R. Staudt, M. Eddaoudi, M.

864

Thommes, Micropor. Mesopor. Mater. 129 (2010) 345. 27 Page 27 of 52

[68] F. Rouquerol, J. Rouquerol, K. Sing, Academic Press, London, 1999.

866

[69] A.V. Neimark, K.S.W. Sing, M. Thommes, in: G. Ertl, H. Knoetzinger, F.

867

Schueth, J. Weitkamp (Eds.), Handbook of Heterogeneous Catalysis, second ed., vol.

868

721, Wiley-VCH Verlag GmbH and Co, KgaA, Weinheim, 2008, pp. 721.

869

[70] K.S. Walton, R. Snurr, J. Am. Chem. Soc. 129 (2007) 8552.

870

[71] T. Duren, F. Millange, G. Ferey, K.S. Walton, R. Snurr, J. Phys. Chem. C 111

871

(2007) 15350.

872

[72] Z.-Y Gu, C-X Yang, N Chang, X-P Yan, Acc. Chem. Res. 45 (2012) 734.

873

[73] Y. Yu, Y. Ren, W. Shen, H. Deng, Z. Gao. Trends Anal. Chem. 50 (2013) 33.

874

[74] B.L. Chen, C.D. Liang, J. Yang, D.S. Contreras, Y.L. Clancy, E.B. Lobkovsky,

875

O.M. Yaghi, S. Dai, Angew. Chem. Int. Ed. 45 (2006) 1390.

876

[75] V. Finsy, H. Verelst, L. Alaerts, D. De Vos, P.A. Jacobs, G.V. Baron, J.F.M.

877

Denayer, J. Am. Chem. Soc. 130 (2008) 7110.

878

[76] Z.-Y. Gu, D.-Q. Jiang, H.-F. Wang, X.-Y. Cui, X.-P. Yan, J. Phys. Chem. C 114

879

(2010) 311.

880

[77] W.O. McReynolds, J. Chromatogr. Sci. 8 (1970) 685.

881

[78] D. Scott, D. Alison, K.J. Praveen, J. Sep. Sci. 34 (2011) 2418.

882

[79] T. Borjigin, F.X. Sun, J.L. Zhang, K. Cai, H. Ren, G.S. Zhu, Chem. Commun. 48

883

(2012) 7613.

884

[80] M.D. Toni, R. Jonchiere, P. Pullumbi, F.-X. Coudert, A.H. Fuchs, Chem. Phys.

885

Chem. 13 (2012) 3497.

887 888 889 890 891 892

cr

us

an

M

d

te

Ac ce p

886

ip t

865

[81] J.H. Cavka, S. Jakobsen, U. Olsbye, N. Guillou, C. Lamberti, S. Bordiga, K.P. Lillerud, J. Am. Chem. Soc. 130 (2008) 13850. [82] B. Bozbiyik, T. Duerinck, J. Lannoeye, D.E. De Vos, G.V. Baron, J.F.M. Denayer, Micropor. Mesopor. Mater. 183 (2014) 143. [83] M.T. Luebbers, T. Wu, L. Shen, R.I. Masel, Langmuir 26 (2010) 11319. [84] I. Gutiérrez, E. Díaz, A. Vega, S. Ordónez, J. Chromatogr. A 1274 (2013) 173. [85] Z.Y. Gu, X.P. Yan, Angew. Chem. Int. Ed. 49 (2010) 1477.

893

[86] G. Ferey, C. Mellot-Draznieks, C. Serre, F. Millange, J. Dutour, S. Surble, I.

894

Margiolaki, Science 309 (2005) 2040.

895

[87] N. Chang, Z.-Y. Gu, X.-P. Yan, J. Am. Chem. Soc. 132 (2010) 13645.

896

[88] N. Chang, X.P. Yan, J. Chromatogr. A 1257 (2012) 116.

897

[89] N. Chang, Z.-Y. Gu, H.-F. Wang, X.-P. Yan, Anal. Chem. 83 (2011) 7094.

28 Page 28 of 52

[90] P.S. Barcia, D. Guimaraes, P.A.P. Mendes, J.A.C. Silva, V. Guillerm, H.

899

Chevreau, C. Serre, A.E. Rodrigues, Micropor. Mesopor. Mater. 139 (2011) 67.

900

[91] L. Fan, X.-P. Yan. Talanta 99 (2012) 944.

901

[92] T.M. Nicholson, S.K. Bhatia, J. Phys. Chem. B 110 (2006) 24834.

902

[93] J.G. Nikelly, Anal. Chem. 44 (1972) 623.

903

[94] J.G. Nikelly, Anal. Chem. 44 (1972) 625.

904

[95] A.S. Münch, J. Seidel, A. Obst, E. Weber, F.O.R.L. Mertens, Chem. Eur. J. 17

905

(2011) 10958.

906

[96] C.-X. Yang, S.-S. Liu, H.-F. Wang, S.-W. Wang, X.-P. Yan, Analyst 137 (2011)

907

133.

908

[97] A.S. Münch, F.O.R.L. Mertens, J. Mater. Chem. 22 (2012) 10228.

909

[98] A.S. Münch, M.S. Lohse, S. Hausdorf, G. Schreiber, D. Zacher, R.A. Fischer,

910

F.O. Mertens, Micropor. Mesopor. Mater. 159 (2012) 132.

911

[99] T. Böhle, F. Mertens, Micropor. Mesopor. Mater. 183 (2014) 162. [100] O.

912

Shekhah, H. Wang, M. Paradinas, C. Ocal, B. Schüpbach, A. Terfort, D. Zacher, R.A.

913

Fischer, C. Wöll, Nat. Mater. 8 (2009) 481.

914

[101] J. Liu, B. Lukose, O. Shekhah, H.K. Arslan, P. Weidler, H. Gliemann, S. Bräse,

915

S. Grosjean, A. Godt, X. Feng, K. Müllen, I.-B. Magdau, T. Heine, C. Wöll, Sci. Rep.

916

2 (2012) 921.

917

[102] J.-H. He, Y.-T. Zhang, Q.-H. Pan, J.-H. Yu, H. Ding, R.-R. Xu, Micropor.

918

Mesopor. Mater. 90 (2006) 145.

920 921 922 923 924 925

cr

us

an

M

d

te

Ac ce p

919

ip t

898

[103] Z.-L. Fanga, S.-R. Zheng, J.-B. Tan, S.-L. Cai, J. Fan, X. Yan, W.-G. Zhang, J. Chromatogr. A 1285 (2013) 132. [104] L. Alaerts, C.E.A. Kirschhock, M. Maes, M.A. van der Veen, V. Finsy, A. Depla, J.A. Martens, G.V. Baron, P.A. Jacobs, J.F.M. Denayer, D.E. De Vos, Angew. Chem. Int. Ed. 46 (2007) 4293. [105] T. Loiseau, C. Serre, C. Huguenard, G. Fink, F. Taulelle, M. Henry, T. Bataille, G. Férey, Chem. Eur. J. 10 (2004) 1373.

926

[106] K. Barthelet, J. Marrot, D. Riou, G. Férey, Angew. Chem. 114 (2002) 291.

927

[107] G. Férey, C. Mellot- Draznieks, C. Serre, F. Millange, J. Dutour, S. Surblé, I.

928

Margiolaki, Science 309 (2005) 2040.

929

[108] S. Miller, P. Wright, C. Serre, T. Loiseau, J. Marrot, G. Férey, Chem. Commun.

930

(2005) 3850.

931

[109] K. Barthelet, J. Marrot, G. Férey, D. Riou, Chem. Commun.( 2004) 520. 29 Page 29 of 52

[110] G. Férey, M. Latroche, C. Serre, F. Millange, T. Loiseau, A. Percheron-Guégan,

933

Chem. Commun. (2003) 2976.

934

[111] S. Bourrelly, P. L. Llewellyn, C. Serre, F. Millange, T. Loiseau, G. Férey, J.

935

Am. Chem. Soc. 127 (2005) 13 519

936

[112] L. Alaerts, M. Maes, P.A. Jacobs, J.F.M. Denayerb, D.E. De Vos, Phys. Chem.

937

Chem. Phys. 10 (2008) 2979.

938

[113] L. Alaerts, M. Maes, L. Giebeler, P.A. Jacobs, J.A. Martens, J.F.M. Denayer,

939

C.E.A. Kirschhock, D.E. De Vos, J. Am. Chem. Soc. 130 (2008) 14170.

940

[114] M. Maes, F. Vermoortele, M. Boulhout, T. Boudewijns, C. Kirschhock, R.

941

Ameloot, I. Beurroies, R. Denoyel, D.E. De Vos, Micropor. Mesopor. Mater. 157

942

(2012) 82.

943

[115] W. De Malsche, S. Van der Perre, S. Silverans, M. Maes, D.E. De Vos, F.

944

Lynen, J.F.M. Denayer, Micropor. Mesopor. Mater. 162 (2012) 1.

945

[116] C.-X. Yang, S.-S. Liu, H.-F. Wang, S.-W. Wang, X.-P. Yan, Analyst 137

946

(2012) 133.

947

[117] S.-S. Liu, C.-X. Yang, S.-W. Wang, X.-P. Yan, Analyst 137 (2012) 816.

948

[118] C.-X. Yang, Y.-J. Chen, H.-F. Wang, X.-P. Yan, Chem. Eur. J. 17 (2011)

949

11734.

950

[119] Y.-Y. Fu, C.-X. Yang, X.-P. Yan. J. Chromatogr. A 1274 (2013) 137.

951

[120] Y.-Y. Fu, C.-X. Yang, X.-P. Yan, Chem. Eur. J. 19 (2013) 13484.

952

[121] S. Han, Y. Wei, C. Valente, I. Lagzi, J.J. Gassensmith, A. Coskun, J.F.

954 955 956 957 958 959

cr

us

an

M

d

te

Ac ce p

953

ip t

932

Stoddart, B.A. Grzybowski, J. Am. Chem. Soc. 132 (2010) 16358. [122] L.-M. Li, H.-F. Wang, X.-P. Yan, Electrophoresis 33 (2012) 2896. [123] V. T. Remcho, Chem. Edu. 2 (1997) 1. [124] Y. Xu, L. Xu, S. Qi, Y. Dong, Z. Rahman, H. Chen, X. Chen, Anal. Chem. 85 (2013) 11369.

[125] S. Feng, C. Pan, X. Jiang, S. Xu, H. Zhou, M. Ye, H. Zou, Proteomics 7 (2007) 351.

960

[126] L.-M. Li, F. Yang, H.-F. Wang, X.-P. Yan. J. Chromatogr. A 1316 (2013) 97.

961

[127] H.-Y. Huang, C.-L. Lin, C.-Y. Wu, Y.-J. Cheng, C.-H. Lin. Anal. Chim. Acta

962

779 (2013) 96.

963

[128] Y.-Y. Fu, C.-X. Yang, X.-P. Yan, Chem. Commun. 49 (2013) 7162.

964

[129] B.Y. Bao, L.J. Broadbelt, R.Q. Snurr, Micropor. Mesopor. Mater. 157 (2012)

965

118. 30 Page 30 of 52

[130] B.Y. Bao, L.J. Broadbelt, R.Q. Snurr, Phys. Chem. Chem. Phys. 12 (2010)

967

6466.

968

[131] S.-M. Xie, X.-H. Zhang, Z.-J. Zhang, M. Zhang, J. Jia, L.-M. Yuan, Anal.

969

Bioanal. Chem. 405 (2013) 3407.

970

[132] S. Xie, B. Wang, X. Zhang, J. Zhang, M. Zhang, L. Yuan, chirality 26 (2014)

971

27.

972

[133] M. Zhang, J.-H. Zhang, Y. Zhang, B.-J. Wang, S.-M. Xie, L.-M. Yuan, J.

973

Chromatogr. A 1325 (2014) 163.

974

[134] X.-H Zhang, S.-M, Xie, A.-H Duan, B.-J Wang, L.-M. Yuan, Chromatographia

975

76 (2013) 831.

976

[135] Z.-Y. Gu, J.-Q. Jiang, X.-P. Yan, Anal. Chem. 83 (2011) 5093.

977

[136] M.T. Luebbers, T. Wu, L. Shen, R.I. Masel, Langmuir 26 (2010) 15625.

978

[137] C.-X. Yang, X.-P. Yan, Anal. Chem. 83 (2011) 7144.

979

Figure Captions

980

Figure 1. Organic linkers of IRMOF-n (n=1 through 7, 8, 10, 12, 14, and 16) labelled

981

appropriately.

982

Figure 2. Chromatograms of alkane mixtures separated on a MOF-508 column: a)

983

separation of n-pentane and n-hexane, b) separation of 2-methylbutane and n-pentane,

984

c) separation of 2,2-dimethylbutane, 2-methylpentane, and n-hexane, and d)

990

Ac ce p

te

d

M

an

us

cr

ip t

966

991

30 control Kováts indices extracted from the literature. Positive values indicate that

992

Cu-BTC provided selectivity for the n-alkanes. Negative values indicate that SE-30

993

provides more selectivity than the Cu-BTC. The limitations are discussed in the text

994

(Reprinted from ref. [78]. Copyright 2011 Wiley-VCH.).

985 986 987 988 989

separation of an alkane mixture containing 2-methylbutane (1), n-pentane (2), 2,2dimethylbutane (3), 2-methylpentane (4), and n-hexane (5). S=thermal conductivity detector response (Reprinted from ref. [74]. Copyright 2006 Wiley-VCH.). Figure 3. Graphic showing the retention selectivity of Lewis-base analytes and other probes. The ordinate values are the retention index (RI) differences between the Kováts indices determined on the 0.75% Cu-BTC experimental column minus the SE-

31 Page 31 of 52

Figure 4. GC separation of xylene isomers and EB on a MIL-101-coated capillary

996

column at 160°C with an N2 flow rate of 3 ml/min (Reprinted from ref. [85].

997

Copyright 2010 Wiley-VCH.).

998

Figure 5. Chromatograms on ZIF-8-coated capillary (20 m long × 0.25 mm i.d.) for

999

GC separation: (a) hexane and its branched isomers and (b) octane and its branched

ip t

995

isomers (Reprinted from ref. [87]. Copyright 2010 American Chemical Society.).

1001

Figure 6. Gas chromatograms of alkane isomers obtained using an UIO-66-coated

1002

capillary column (20 m long × 0.25 mm i.d.) using a temperature program (100°C for

1003

1 min, then 10°C.min-1 to 200°C) (Reprinted from ref. [88]. Copyright 2012

1004

Elsevier.).

1005

Figure 7. Chromatograms on MIL-100(Fe) (6 mg.ml-1) (a,b) and MIL-100(Cr) (6

1006

mg.ml-1) (c,d) coated capillary columns (20 m long × 0.25 mm i.d.): (a,c) C6 group:

1007

2,2-C4 (2,2-dimethybutane), cyclo-C6 (cyclohexane), 2,3-C4(2,3-dimethybutane), 2-

1008

C5(2-methypentane), and C6 (hexane) with an N2 flow rate of 1.0 ml/min at 80°C and

1009

(b, d) C7 group: 2,2,3-C4 (2,2,3-trimethybutane), 3,3-C5 (3,3-dimethypentane), 2,3-

1010

C5 (2,3-dimethypentane), 2-C6 (2-methyhexane) and C7 (heptane) with an N2 flow

1011

rate of 1.0 ml/min at 110°C (Reprinted from ref. [91]. Copyright 2012 Elsevier.).

1012

Figure 8. Comparison of two chromatograms of natural gas (Freiberg, Germany,

1013

April 2010) obtained using the MOF-5-CSA-coated column (black line) and an

1019

Ac ce p

te

d

M

an

us

cr

1000

1020

injector: split: 5.1:1 at 250°C; detector: FID at 250°C (Reprinted from ref. [95].

1021

Copyright 2011 Wiley-VCH.).

1022

Figure 9. Gas chromatograms on an MOF-CJ3-coated capillary (10 m long × 0.32

1023

mm i.d.) for separation of alkanes with FID for detection: (A) linear alkanes with an

1024

N2 flow using a temperature program of 80°C for 1 min, then 20°C.min-1 to 180°C;

1025

(B) n-pentane, dimethylbutane, 2-methylpentane and n-hexane with an N2 flow at

1014 1015 1016 1017 1018

Al2O3-based, Na2SO4-deactivated commercial PLOT column (Agilent HP-PLOT “S”) (gray). MOF-5-CSA-coated column: (10 m long × 0.53 mm i.d.) with 1-mm coating thickness. Carrier gas: He; flow rate: 9.96 ml/min; oven: 80°C for 0.01 min and 80– 140°C at 60°C/min for 1 min; injector: split: 5.1:1 at 250°C; detector: FID at 250°C; HP-PLOT “S”: (15 m long × 0.53 mm i.d.) with 15-mm coating thickness; carrier gas: He; flow: 9.93 ml/min; oven: 90°C for 0.01 min and 90–130°C at 40°C/min for 1 min;

32 Page 32 of 52

40°C; (C) n-hexane, isooctane and n-heptane with an N2 flow at 40°C; (D) isooctane,

1027

n-heptane and octane with an N2 flow at 40°C (Reprinted from ref. [103]. Copyright

1028

2013 Elsevier.).

1029

Figure 10. Chromatographic separation of a mixture of EB, m-xylene, and p-xylene

1030

on a column packed with MIL-47 in the liquid phase and hexane as the desorbent at

1031

298 K. The signal intensity of the refractive index detector is shown versus the eluted

1032

volume. (Reprinted from ref. [104]. Copyright 2007 Wiley-VCH.).

1033

Figure 11. Chromatographic separation of a mixture of (a) ethyltoluene isomers on a

1034

column packed with MIL-47 and (b) ethyltoluene isomers on a column packed with

1035

MIL-53 and hexane as the desorbent at 25°C. The signal intensity of the RID is shown

1036

versus the eluted volume. The curves have been corrected for the dead volume of the

1037

column (Reprinted from ref. [113]. Copyright 2008 American Chemical Society.).

1038

Figure 12. Influence of the temperature on the retention time of ethylbenzene, p-

1039

xylene and oxylene (2.25 × 10-4 M, 400 nl), at a flow rate of 1.5 μl/min (mobile phase

1040

75/25 AN/1-propanol). The chromatograms are gradually shifted by 2 units for clarity.

1041

The arrow indicates the injection induced disturbance in the baseline (Reprinted from

1042

ref. [115]. Copyright 2012 Elsevier.).

1043

Figure 13. HPLC separation of the fullerenes in the toluene solution of carbon soot

1044

(2.63 mg.ml-1) on a MIL-101-packed column (5 cm long × 4.6 mm i.d.) at room

1046 1047 1048 1049 1050

cr

us

an

M

d

te

Ac ce p

1045

ip t

1026

temperature with CH2Cl2/CH2CN (98:2) as the mobile phase at a flow rate of 1 ml.min-1 with UV detection at 340 nm (Reprinted from ref. [118]. Copyright 2011 Wiley-VCH.).

Figure 14. Reproducibility of the chromatograms for HPLC on a MIL-100(Fe)packed column (5 cm long × 4.6 mm i.d.): (A) benzene, toluene, ethylbenzene, naphthalene and 1-chloronaphthalene (5 μl, 0.01 mol.l-1) using MeOH/H2O (43:57) as

1051

the mobile phase; (B) aniline, acetanilide, 2-nitroaniline and 1-naphthylamine (5 μl,

1052

0.01 mol.l-1) using MeOH/H2O (43:57) as the mobile phase; (C) o-, m-, and p-

1053

chloroaniline (5 μl, 0.012 mol.l-1) using DCM/MeOH (99.7:0.3) as the mobile phase;

1054

(D) o-, m-, and p-toluidine (5 μl, 0.012 mol.l-1) using DCM/MeOH (99.7:0.3) as the

1055

mobile phase at a flow rate of 0.5 ml.min-1. All separations were performed at room

33 Page 33 of 52

temperature and monitored using a UV detector at 254 nm (Reprinted from ref. [119].

1057

Copyright 2013 Elsevier.).

1058

Figure 15. Nano-UHPLC chromatograms of aromatic acids separated on a MIL-

1059

101(Cr)–polymer monolith (a) and a neat polymer monolith (b). The separation

1060

conditions were a mobile phase of 0.1% formic acid in water/0.1% formic acid in

1061

ACN = 20/80 (v/v), a flow rate of 1 μl.min-1, a detection wavelength of 200 nm, an

1062

injection volume of 500 nl, an effective length of 35 cm, a column temperature of

1063

25°C, and an analyte concentration of 10 μg.ml-1. 1 (benzoic acid), 2

1064

(terephthalaldehydic acid), 3 (isophthalic acid), 4 (terephthalic acid) (Reprinted from

1065

ref. [127]. Copyright 2013 Elsevier.).

us

cr

ip t

1056

an

1066 1067

M

1068

te Ac ce p

1070

d

1069

34 Page 34 of 52

*Highlights (for review)

Review Highlights: 

Introduction about metal-organic frameworks and it superior characterization over the

ip t

conventional stationary phases in chromatography. Structural overview about metal-organic frameworks.



Applications of metal-organic frameworks in Gas Chromatography as a stationary phase

cr



us

in both packed and coated capillary columns.

Applications of metal-organic frameworks in High-Performance Liquid Chromatography.



Applications of metal-organic frameworks in other chromatographic techniques.

Ac ce p

te

d

M

an



Page 35 of 52

Figure

Figure 1 O-

O-

O Br

O

OO

NH2

O-

O

O-

R2-BDC (IRMOF-2)

R1-BDC (IRMOF-1)

O-

O

O

O-

O

O

O

O

O

O-

O

O

O

O-

R6-BDC (IRMOF-6)

R5-BDC (IRMOF-5)

-

O

O-

O

R4-BDC (IRMOF-4)

R3-BDC (IRMOF-3)

O-

O

O-

O

O-

us

O-

O-

an

O

O O

-

O-

O O

O O

O-

O

ip t

O

cr

O-

O

O

O-

-

O

BPDC (IRMOF-10)

O-

HPDC (IRMOF-12)

O

O-

PDC (IRMOF-14)

TPDC (IRMOF-16)

te

d

M

2, 6-NDC (IRMOF-8)

Ac ce p

R7-BDC (IRMOF-7)

Page 36 of 52

Figure

Ac ce p

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Figure 2

Page 37 of 52

Figure

Ac ce p

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d

M

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cr

ip t

Figure 3

Page 38 of 52

Figure

Ac ce p

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d

M

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cr

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Figure 4

Page 39 of 52

Figure

Ac ce p

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M

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Figure 5

Page 40 of 52

Figure

Ac ce p

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d

M

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cr

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Figure 6

Page 41 of 52

Figure

Ac ce p

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M

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Figure 7

Page 42 of 52

Figure

Ac ce p

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Figure 8

Page 43 of 52

Figure

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Figure 9

Page 44 of 52

Figure

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Figure 10

Page 45 of 52

Figure

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Figure 11

Page 46 of 52

Figure

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Figure 12

Page 47 of 52

Figure

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Figure 13

Page 48 of 52

Figure

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Figure 14

Page 49 of 52

Figure

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Figure 15

Page 50 of 52

ip t

Table 1 The most significant applications of metal-organic frameworks in chromatography. Pore Pore Thermal opening diameter stability (A°) (A°) (C°) Gas chromatography 4 360

surface area (g.cm-3)

MOF-508, Zn (BDC)(4,4'-Bipy)0.5

946

MOF-5, IRMOF-1 (Zn4O(BDC)3)

630-3046

7.5, 11.2

11, 15

IRMOF-3, (Zn4O(NH2-BDC)3) IRMOF-8, (Zn4O(2,6-NDC)3) IRMOF-10, (Zn4O(BPDC)3)

1957 1362 265

9.6 12.5 16.7

41.8 132.6

320 300 300

HKUST-1, MOF-199, (Cu3(BTC)2)

404-629

8, 9

12

220-280

8.5 5.5-8.6 5.5-8.6

8.5 25-29 25-29

350 280 280

12, 16

29, 34

300-330

2.9

4.3

480

3.4

11.4

380-550

800 2040 2153

MIL-101(Cr), (Cr3O(H2O)2F(BDC)3)

2736-2907

ZIF-7, (Zn(benzimidazolate)2) ZIF-8, Zn(2-methylimidazole)2 JUC-110, ([Cd(H-thipc)2].6H2O)

1504

ce pt

UiO-66, [Zr6O4(OH)4(BDC)6]

ed

MIL-47(V), (V O(BDC)) MIL-100(Fe), ([(Fe3OF3(BDC)3)]. nH2O) MIL-100(Cr), ([(Cr3OF3(BDC)3)]. nH2O)

MOF-CJ3 [HZn3(OH)(BTC)2(2H2O) (DMF)] . H2O DMOF-1, [Cu2(BDC)2(DABCO)]

MIL-101(Cr), (Cr3O(H2O)2F(BDC)3)

2736-2907

Ac

750

940-1038 1598

ZIF-8, Zn(2-methylimidazole)2

1652 alone, 565 with SiO2

1947

MIL-100(Fe), ([(Fe3OF3(BDC)3)]. nH2O)

250

High performance liquid chromatography 8.5 8.5 330-385 pore volume of 0.32 cm3.g-1

12, 16

29, 34

8.5

8.5

5, 9

300-330 330-385

1700 alone, 423 with Polymer

MIL-101(Cr), (Cr3O(H2O)2F(BDC)3)

2938 alone, 732 with Polymer

25, 29 5.72, 17.9

320 280

pore volume of 0.48 cm3.g-1

Other chromatographic methods 7.5, 11.2 11, 15 400-480 3.4 11.6 ≈450 5, 9

CAU-1, ([Al8(OH)4-(OCH3)8(BDC-NH2)6])

Form

Ref.

Year

Alkanes Xylene Isomers & EB VOCs(b) Natural gases n-Alkanes POPs(a) VOCs POPs VOCs VOCs small Lewis-base analytes small hydrocarbons Xylene Isomers & EB Alkane isomers Alkane isomers Xylene Isomers & EB n-Alkanes n-Alkanes n-Alkanes organic vapors and gases Branched & Linear Alkanes n-Alkanes Alcohols from water Alkanes & Alkylbenzenes n-hexane & cyclohexane Alkanes & aromatic positional isomers Light hydrocarbons

Packed column Packed column Packed column Coated capillary Coated capillary Coated capillary Packed column Coated capillary Packed column Packed column Packed column Coated capillary Packed column Coated capillary Coated capillary Coated capillary Coated capillary Coated capillary Coated capillary Packed column Coated capillary Coated capillary Packed column Coated capillary Packed column

[74] [76] [83] [95] [89] [135] [84] [135] [84] [84] [78] [97] [75] [91] [91] [85] [89] [87] [89] [136] [87] [89] [79] [88] [82]

2006 2010 2010 2011 2011 2011 2013 2011 2013 2013 2011 2012 2008 2012 2012 2010 2011 2010 2011 2010 2010 2011 2012 2012 2013

Coated capillary

[103]

2013

Coated capillary

[99]

2013

Xylene Isomers & EB

Packed column

[104]

2007

Substituted aromatics Fullerenes Alkylaromatics Positional isomers Wide range of analytes Several analytes Endocrine disrupting chemicals and pesticides

Packed column Packed column Packed column Packed column Packed column Packed column core–shell microspheres packed column ZIF-8@SiO2

[137] [118] [113] [116] [117] [119]

2011 2011 2008 2012 2012 2013

[120]

2013

organic dyes phenolic isomers

Single crystal PSP(c) for C-EKC(d)

[121] [122]

2010 2012

Small Organic Molecules

Coated capillary for CEC(e)

[124]

2013

[126]

2013

[127]

2013

us

11.6

≈200 480-540

pore volume of 0.50 cm3.g-1

MIL-100(Fe), ([(Fe3OF3(BDC)3)]. nH2O)

MOF-5, IRMOF-1 (Zn4O(BDC)3) ZIF-8, Zn(2-methylimidazole)2

11.6

8-11 7.5-11

1026-1300

MIL-47(V), (VIVO(BDC))

MIL-53(Al), (AlIII(OH)(BDC))

4.5 5-7

614.3 525

400-480

M an

IV

Samples

cr

MOF material

25, 29 4.5, 10

Aromatic carboxylic acids & some model drugs Various aromatics

(f)

Composite with P-MA Coated capillary for CEC Composite with PMA monolithic capillary for CEC & nano-LC

Page 51 of 52

ip t

Composite with PMA [128] monolithic column for HPLC 250 racemates Chiral GC separation [131] Co(D-Cam)1/2(BDC)1/2(tmdpy) 350 racemates Chiral GC separation [134] Zn(ISN)2.2H2O 250 racemates Chiral GC separation [132] Ni(D-Cam)(H2O)2 19.4, 22.4 5 racemates Chiral HPLC separation [133] [Cu2(D-Cam)2(4,4′-bpy)]n (a) Persistent Organic Pollutants, (b) volatile organic compounds, (c) pseudostationary phase, (d) Capillary Electrokinetic chromatography, (e) Capillary Electrochromatography, (f) poly-methacrylate 881 alone, 321 with Polymer

Various aromatics

2013 2013 2013 2014 2014

Ac

ce pt

ed

M an

us

cr

UiO-66, [Zr6O4(OH)4(BDC)6]

Page 52 of 52